Deposits of ores generally contain more than one valuable mineral. To be sold as separate products, the valuable minerals must be separated from each other. Also, valuable minerals must be separated from less valuable minerals and host rock. Such less valuable minerals and host rock are frequently referred to as gangue. For example, copper sulfide and iron sulfide ores are often present together with sulfides of other metals such as zinc and lead, and these minerals are generally found in their natural state associated with gangue materials.
Froth flotation processes are one means used to concentrate and recover desired valuable minerals. Such processes can be used to separate one valuable mineral from another and to separate valuable minerals from gangue. Froth flotation processes are based upon the affinity of particles of a given mineral for bubbles under certain conditions. The bubbles attract and float one or more minerals while other minerals or gangue material sink.
In conventional froth flotation, the ore is ground into fine particles. The fine particles are admixed with a flotation fluid such as water, brine, etc., to form a pulp. A froth is formed by agitating the pulp while passing a gaseous stream such as air through the pulp.
Various reagents can be added to the pulp to aid in forming the froth, floating certain minerals, preventing the flotation of certain minerals, etc. These reagents are often broadly referred to as flotation process aids or flotation agents. These reagents include frothers, collectors, activators, pH regulators, flocculents, dispersants, and depressants.
Frothers are reagents which can be used in ore flotation to aid in forming bubbles and a stable froth in which the minerals to be recovered are collected. Typical frothers are pine oil, methyl isobutyl carbinol and poly(propylene glycol)methylethers.
Collectors can be added to a flotation process to assist in the concentration of a mineral in the froth. Generally, collectors create an affinity between a bubble and a particular mineral particle. The bubble then can buoy the mineral particle to the surface of the flotation fluid. Different collectors are preferably used for different minerals, for example, sulfides of lead, zinc, copper and nickel can be collected and floated by short-chain hydrocarbons (C.sub.2 -C.sub.5) of the sulfhydryl type. Oxide minerals, on the other hand, are typically collected and floated by long-chain (C.sub.12 -C.sub.18) fatty acids, sulfonates, and amines.
Activators can be added to flotation processes to obtain improve collector attachment to the mineral to be floated. The activators generally interact with or are attached to the mineral to be floated. The activator also can interact with or attach to the collector and thus serve as an intermediate for flotation. For instance, copper sulfate is known to activate zinc and thus aid in the flotation of zinc in some circumstances.
A pH regulator can be added to a pulp to control the ionization of a collector from its molecular to its ionic species. This can affect the forces of attraction or repulsion between a collector and a mineral, absorption of the collector to the mineral, and/or flotation. Various pH regulators such as acidic or basic compounds are known in the art.
A dispersant can be added to a flotation system to ensure that co-flocculation of a desired mineral and gangue does not occur. Lignin sulfonates, sodium silicate, tannin, and others are typical dispersants.
A flocculent can be added to a flotation step to cause agglomeration of only desired particles. The floccules can then be removed by froth flotation. Known flocculents include starches and gums.
A depressant can be added to a flotation system to prevent or reduce the flotation of a certain mineral. Depressants are frequently referred to as suppressants. A specific depressant can selectively prevent or reduce assimilation in the froth of a certain mineral or group of minerals or gangue materials.
For example, in the recovery of copper sulfide, lime can be added as a depressant. Lime can depress pyrite which is frequently present in significant quantities in copper sulfide ores.
Also, certain depressants are known to selectively depress copper sulfide in the recovery of other minerals under certain flotation conditions. Sodium thiophosphate, U.S. Pat. No. 2,811,255; thioglycolic acid, U.S. Pat. No. 2,449,984; and thioglycerol, U.S. Pat. No. 3,785,488 are known copper sulfide depressants.
Also it is known in the art, for example, to use sodium cyanide to selectively depress sulfides of copper and iron while allowing lead sulfide to float.
Thus, although many disclosures and much improvement has been made in the field of depressants utilized in recovery of minerals, there is considerable room for further improvement. For instance, there is a need for depressants which will selectively depress sulfides of lead and zinc while permitting minerals containing copper or iron to float.